It seems that Google is testing a small change to the search results. This particular test is focused around not displaying the line break or line separator between the search ads at the top of the search results and the organic listings below the ads.
This test was discovered by a reader, Frederik Hyldig, who provided Search Engine Land with screen shots. Here is an animated gif showing the difference between what we normally, and currently, see and what is being tested.
It’s also known that Google tested bolder separators between the paid search ads and organic results about a couple months ago.
As of this writing, I was unable to replicate the results that Frederik got.